flatpak: Give dconf access

This is needed for the GTK inspector to work.
7 jobs for gtk-inspector in 9 minutes and 9 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Build
passed #192513
librem5
build-debian-clang

00:03:27

passed #192511
librem5
build-debian-gcc

00:02:39

passed #192512
librem5
build-debian-gcc-static

00:02:33

passed #192514
librem5
build-fedora-gcc

00:03:36

 
  Docs
passed #192515
librem5
build-gtkdoc

00:01:44

 
  Test
passed #192516
librem5
unit-test

00:01:36

46.2%
 
  Package
passed #192517
librem5
package-debian

00:02:11